1. Field of the Invention
The present invention relates generally to a flow cell used to hold a liquid sample to be analyzed by a reflectance or fluorescence-type analyzer and, more particularly, to such a cell having a flow-through design to permit accurate and precise real-time analysis of a liquid sample stream where continuous low volume flows are required.
2. Description of the Prior Art
Many industrial operations require constant monitoring and analysis to maintain systems control, optimize processes, and monitor generated waste output. With today's demanding standards for quality and statistical process control in the industrial environment, reliable analytical results are critical for success and maintaining profit. As a result, the use of on-line analyses for process control and industrial-stream monitoring has increased rapidly in recent years. On-line analysis of process streams eliminates excess lag time between sampling and circuit adjustments. Critical analytical information is provided in real time, thus helping maintain optimum process conditions and eliminating excess losses. In addition, multi-element on-line analyses provides additional control parameters to maintain process stream purity and minimize hazardous waste production.
The principal challenge for on-line, real-time analysis is to transfer the analytical method and measurement technique from an operator-intensive batch mode to an automated continuous mode. Appropriate methods require that the analyzer not perturb the sample stream, analysis speed be comparable to the process response time, and the analyzer be reliable for harsh industrial environments.
Energy-dispersive x-ray fluorescence (EDXRF) techniques have been successfully used for many years for on-line elemental analysis of solids, slurries, and liquids. There are significant advantages of portable EDXRF instrumentation over currently used large-scale industrial instrumentation. Commercially installed, on-line EDXRF units typically cost between $100,00 and $200,000 depending on the automation level, application, and configuration. In contrast, bench-top EDXRF models cost between $20,000 to $30,000. Besides lower cost, bench-top models provide portability and flexibility for a variety of industrial applications. In contrast, the large-scale industrial systems are usually non-mobile, permanently installed, and primarily dedicated to a specific application. However, a limitation of portable, bench-top units is the explicit design for manual, batch sampling without on-line capability.
Flow-through sampling cells exist for many different analytical applications, including industrial grade EDXRF on-line instrumentation. However, the lack of EDXRF specialized low-volume flow cells for laboratory and small-scale pilot plant situations render bench-top instruments useless for on-line applications. Real-time changes within the process streams require a representative sample be constantly present at the EDXRF instrument's sample window which has a large diameter surface. Industrial grade flow cells for large-scale industrial processes require gallons of sample per minute, an impractical solution for small streams using low-volume flows. Consequently, there is a need for a flow through cell for bench-top EDXRF instruments to replace the individual sample cups and which is designed for low-volume streams and which allows for rapid response to real-time process stream changes.